Background: Antimicrobial resistance is an increasing problem and reducing AM use is critical in limiting its severity. The underlying causes of antimicrobial use at pig farm level must be understood to select effective reduction measures. We previously showed that antimicrobial use on Swedish pig farms is comparatively low but varies between farms, although few farms are high users. In the present survey of a convenience sample of 60 farrow-to-finish herds in Sweden, we investigated farmers&rsquo; attitudes to antimicrobials and the influence of information provided by veterinarians about antimicrobial resistance. Farm characteristics were also recorded. We had previously quantified antimicrobial use for different age categories of pigs during one year, as well as external and internal biosecurity. Risk factors based on hypothetical causal associations between these and calculated treatment incidence (TI) for the different age categories were assessed here in a linear regression model.

Results: There were no significant associations between biosecurity and TI for any pig age category. Increasing farmer age was associated with higher TI for suckling piglets and fatteners. For suckling piglets, the age group with the highest frequency of treatment, TI was also significantly associated with farmer and education of the staff, where female farmers, and university educated staff was associated with a higher TI. Larger farms were associated with a higher TI in fatteners.

Conclusions: In the investigated Swedish pig farms, factors that influenced antimicrobial usage were more related to characteristics of the individual farmer and his/her staff than to biosecurity level, other management factors or farmers&rsquo; attitudes to antimicrobials.

Mentions:
A directed acyclic graph (DAG) illustrating the hypothetical causal associations between assumed risk factors and frequency of AM use (expressed as TI) is shown in Fig. 1. Herd characteristics considered for the linear regression models were: number of sows, number of employees, whether the farm was specific pathogen free (SPF) or not, and average reported age at weaning. Individual characteristics were age, gender and years of experience of the farmer, and highest level of education of the staff. Attitudes considered important were the four constructs (perceived benefits of AM, perceived risks of AM, perceived need for AM and information contribution from veterinarians). All candidate risk factors, except gender, level of education and SPF status, were measured on a continuous scale and the assumption of linear associations with the outcome was managed by introducing a quadratic term after centring on the mean, which was retained in the model if it was statistically significant (p < 0.05). Multicollinearity between the potential predictor variables was assessed by Spearman rank correlations. SPF status was found to be highly correlated with external biosecurity and was excluded from the model, because external biosecurity was better distributed and was of primary interest in this study. Number of employees was highly correlated with number of sows and only the latter was retained in the regression models. All TI values were log-transformed (natural base) to achieve normally distributed residuals, where 1 was added to all TI values for weaners, fatteners and adults to avoid taking the log of zero.Fig. 1

Mentions:
A directed acyclic graph (DAG) illustrating the hypothetical causal associations between assumed risk factors and frequency of AM use (expressed as TI) is shown in Fig. 1. Herd characteristics considered for the linear regression models were: number of sows, number of employees, whether the farm was specific pathogen free (SPF) or not, and average reported age at weaning. Individual characteristics were age, gender and years of experience of the farmer, and highest level of education of the staff. Attitudes considered important were the four constructs (perceived benefits of AM, perceived risks of AM, perceived need for AM and information contribution from veterinarians). All candidate risk factors, except gender, level of education and SPF status, were measured on a continuous scale and the assumption of linear associations with the outcome was managed by introducing a quadratic term after centring on the mean, which was retained in the model if it was statistically significant (p < 0.05). Multicollinearity between the potential predictor variables was assessed by Spearman rank correlations. SPF status was found to be highly correlated with external biosecurity and was excluded from the model, because external biosecurity was better distributed and was of primary interest in this study. Number of employees was highly correlated with number of sows and only the latter was retained in the regression models. All TI values were log-transformed (natural base) to achieve normally distributed residuals, where 1 was added to all TI values for weaners, fatteners and adults to avoid taking the log of zero.Fig. 1

Background: Antimicrobial resistance is an increasing problem and reducing AM use is critical in limiting its severity. The underlying causes of antimicrobial use at pig farm level must be understood to select effective reduction measures. We previously showed that antimicrobial use on Swedish pig farms is comparatively low but varies between farms, although few farms are high users. In the present survey of a convenience sample of 60 farrow-to-finish herds in Sweden, we investigated farmers&rsquo; attitudes to antimicrobials and the influence of information provided by veterinarians about antimicrobial resistance. Farm characteristics were also recorded. We had previously quantified antimicrobial use for different age categories of pigs during one year, as well as external and internal biosecurity. Risk factors based on hypothetical causal associations between these and calculated treatment incidence (TI) for the different age categories were assessed here in a linear regression model.

Results: There were no significant associations between biosecurity and TI for any pig age category. Increasing farmer age was associated with higher TI for suckling piglets and fatteners. For suckling piglets, the age group with the highest frequency of treatment, TI was also significantly associated with farmer and education of the staff, where female farmers, and university educated staff was associated with a higher TI. Larger farms were associated with a higher TI in fatteners.

Conclusions: In the investigated Swedish pig farms, factors that influenced antimicrobial usage were more related to characteristics of the individual farmer and his/her staff than to biosecurity level, other management factors or farmers&rsquo; attitudes to antimicrobials.